JP6581643B2 - Ball screw spline - Google Patents

Description

  The present invention relates to a ball screw spline used for, for example, a Zθ actuator of an industrial robot.

  For example, a ball screw spline may be used for a Zθ actuator used for a tip axis of an industrial robot in order to meet the demand for higher functionality and higher accuracy. This ball screw spline includes a shaft, a ball screw nut assembled to the shaft, and a ball spline outer cylinder assembled to the shaft. The shaft performs arbitrary linear motion (Z), rotational motion (θ), and spiral motion (Z + θ) by giving rotational inputs to the ball screw nut and the ball spline outer cylinder to control the amount of rotation.

  A spiral ball screw groove and a linear ball spline groove are formed on the shaft so as to intersect each other. The ball screw nut assembled to the shaft has a spiral ball screw groove facing the ball screw groove of the shaft and circulates a screw ball that engages with the ball screw groove of the shaft. The ball spline outer cylinder assembled to the shaft has a linear ball spline groove facing the ball spline groove of the shaft and circulates spline balls that engage with the ball spline groove of the shaft.

  In order to operate the ball screw spline smoothly, the screw ball that rolls the ball screw groove enters the ball spline groove at the intersection of the spiral ball screw groove and the linear ball spline groove of the shaft. It is necessary not to. Further, it is necessary to prevent spline balls rolling in the ball spline grooves from entering the ball screw grooves. For this reason, in the conventional ball screw spline, the depth of the ball screw groove of the shaft is made deeper than the depth of the ball spline groove (see Patent Document 1). This is to prevent the screw ball rolling in the ball screw groove from moving over the step between the ball screw groove and the ball spline groove and shifting to the ball spline groove. On the other hand, the spline balls are held by the cage of the ball spline outer cylinder, and even if the ball spline outer cylinder is pulled out from the shaft, it does not fall off from the ball spline outer cylinder. For this reason, the spline ball rolling in the ball spline groove does not move to the ball screw groove at the intersection.

  Further, in the conventional ball spline, since the ball diameter is dominantly determined by the depth of the groove, along with making the depth of the ball screw groove of the shaft deeper than the depth of the ball spline groove, The diameter of the screw ball is larger than the diameter of the spline ball.

JP-A-62-165057

  In recent years, there has been a demand for lower inertia of the ball screw spline, that is, to reduce the size and weight of the ball screw spline. For example, if the ball screw spline used for the tip shaft of an industrial robot can be reduced in size and weight, the industrial robot can be moved at high speed, and the motor can be reduced in size.

  However, in the conventional ball screw spline, there is a problem that the ball screw spline is limited in size and weight because it is necessary to satisfy the above-described condition of the intersection of the ball screw groove and the ball spline groove of the shaft. .

  Therefore, an object of the present invention is to provide a ball screw spline that can be reduced in size and weight.

In order to solve the above problems, one embodiment of the present invention is directed to an axis formed so that a spiral ball screw groove and a linear ball spline groove intersect each other, and the ball screw groove of the axis facing the ball screw groove. A ball screw nut having a spiral ball screw groove that enables the ball for threading engagement with the ball screw groove of the shaft to be circulated, and a linear ball spline facing the ball spline groove of the shaft A ball spline outer cylinder having a groove and enabling circulation of a spline ball that engages with the ball spline groove of the shaft, the depth of the ball screw groove of the shaft being determined by the ball spline of the shaft the above depth of the grooves, the diameter of the ball for the screw and smaller than the diameter of the ball the spline, the ball screw of the depth of the ball screw groove of the shaft the ball screw nut Deeper than the depth of the shaft, the BCD ball screw with a ball the ball screw nut and the screw, a ball screw spline larger than the diameter of the shaft.
According to another aspect of the present invention, there is provided a shaft formed such that a spiral ball screw groove and a linear ball spline groove intersect each other, and a spiral ball screw groove facing the ball screw groove of the shaft A ball screw nut that enables circulation of a screw ball that engages with the ball screw groove of the shaft, and a linear ball spline groove that faces the ball spline groove of the shaft. A ball spline outer cylinder that enables circulation of a spline ball that engages with the ball spline groove, and the ball screw nut has the ball screw groove formed therein and a through-hole penetrating in the axial direction. a nut body that is provided at an end portion in the axial direction of the nut main body, and a circulating member having a direction changing passage which is connected to the through hole and the ball screw groove of the nut main body, The depth of the ball screw groove of the serial axis than depth of the ball spline groove of the shaft, the diameter of the ball for the screw and smaller than the diameter of the ball the spline, the ball screw groove of the shaft It is a ball screw spline which makes the depth deeper than the depth of the ball screw groove of the ball screw nut .

  According to the present invention, the diameter of the ball for screw is made smaller than the diameter of the ball for spline even though the depth of the ball screw groove of the shaft is not less than the depth of the ball spline groove. Due to the difference in the circulation structure between the ball screw nut and the ball spline outer cylinder, the outer diameter of the ball screw nut tends to be larger than that of the ball spline outer cylinder. This is because the ball screw nut deflects the screw ball that rolls the spiral ball screw groove of the shaft in the tangential direction, whereas the spline nut splines that rolls the linear ball spline groove of the shaft. This is because the working ball can be deflected near the axis. According to the present invention, since the diameter of the screw ball is made smaller than the diameter of the spline ball, the outer diameters of both the ball screw nut and the ball spline outer cylinder can be reduced in a balanced manner. Can be reduced in size and weight.

It is a perspective view of a ball screw spline incorporating a screw nut and a spline nut of an embodiment of the present invention (an example in which the screw nut is disposed on the front side). It is a perspective view of a ball screw spline incorporating a screw nut and a spline nut of the present embodiment (an example in which the spline nut is disposed on the front side). It is an external appearance perspective view of the axis | shaft of this embodiment. 4A is a cross-sectional view perpendicular to the axis of the present embodiment, and FIG. 4B is an enlarged view of a portion b of FIG. 4A. It is an enlarged perspective view of a ball screw nut and a shaft of this embodiment (a part of a ball screw nut is notched). It is an expansion perspective view of the ball screw nut of this embodiment (a part of lid member is notched). Fig.7 (a) is sectional drawing along the axial line of the nut main body and axis | shaft of this embodiment, FIG.7 (b) is the b section enlarged view of Fig.7 (a). It is an expansion perspective view of the ball spline outer cylinder and axis of this embodiment (a part of ball spline outer cylinder is notched). It is an axis perpendicular sectional view of a ball spline outer cylinder and a shaft of this embodiment.

  Hereinafter, a ball screw spline according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the ball screw spline of the present invention can be embodied in various forms, and is not limited to the embodiments described herein. This embodiment is provided with the intention of enabling those skilled in the art to fully understand the scope of the invention by fully disclosing the specification.

  1 and 2 are perspective views (partially sectional views) of a ball screw spline according to an embodiment of the present invention. FIG. 1 shows an example in which a ball screw nut 2 (hereinafter simply referred to as a nut 2) is disposed on the front side, and FIG. 2 illustrates a ball spline outer cylinder 3 (hereinafter simply referred to as an outer cylinder 3) disposed on the near side. It is an example. 1 and 2, 1 is a shaft, 2 is a nut, and 3 is an outer cylinder. Reference numeral 23 denotes a bearing that rotatably supports the nut 2, and reference numeral 33 denotes a bearing that supports the outer cylinder 3 to rotate three times. Bearings 23 and 33 are attached to the housing of the Zθ actuator. For example, a pulley (not shown) is attached to the nut 2 and the outer cylinder 3 so that a rotational input can be given to the nut 2 and the outer cylinder 3. Below, the axis | shaft 1, the nut 2, and the outer cylinder 3 are demonstrated in order.

  As shown in FIG. 1, a spiral ball screw groove 1 a (hereinafter simply referred to as a screw groove 1 a) having a predetermined lead is formed on the outer surface of the shaft 1. A linear ball spline groove 1b (hereinafter simply referred to as a spline groove 1b) extending in the axial direction is formed on the outer surface of the shaft 1. In this embodiment, the number of threads of the thread groove 1a is 1, and the number of threads of the spline groove 1b is 4, but these numbers are appropriately set according to the specifications.

  FIG. 3 shows an external perspective view of the shaft. The thread groove 1a has a cross-sectional shape perpendicular to the groove in a Gothic arch shape. The spline groove 1b includes a ball rolling portion 1b1 facing the spline ball 37 (see FIG. 2), and a cage facing portion 1b2 facing the cage 41 (see FIG. 9) adjacent to the ball rolling portion 1b1. Have.

  FIG. 4 shows a cross-sectional view perpendicular to the axis. In a cross-sectional view perpendicular to the axis, the thread groove 1a is substantially linear. 1a1 is an edge of the thread groove 1a, and 1a2 is a bottom of the thread groove 1a. The ball rolling part 1b1 of the spline groove 1b has a circular arc shape in cross section. The cage facing portion 1b2 of the spline groove 1b has a substantially L-shaped cross section. The cage facing portion 1b2 can be made deeper or shallower than the ball rolling portion 1b1. The spline groove 1b can also be composed of only the ball rolling part 1b1.

  As shown in FIG. 3, the thread groove 1a and the splan groove 1b intersect at the A portion. At the intersecting portion A, the thread groove 1a is deeper than the spline groove 1b, and the thread groove 1a is inside the shaft 1 more than the spline groove 1b. In other words, as shown in FIG. 4, the root diameter r1 of the thread groove 1a (the radius r1 from the center O of the shaft 1 to the bottom 1a2 of the thread groove 1a) is the root diameter r2 of the spline groove 1b (from the center O of the shaft 1). It is smaller than the radius r2) to the bottom of the spline groove 1b.

  As shown in FIG. 3, since the thread groove 1a is deeper than the spline groove 1b, the screw ball 27 (see FIG. 1) rolling on the thread groove 1a gets over the step between the thread groove 1a and the spline groove 1b. Thus, the transition to the spline groove 1b is prevented. On the other hand, the spline ball 37 is held by the retainer 41 (see FIG. 9) of the outer cylinder 3, and does not fall off the outer cylinder 3 even if the outer cylinder 3 is pulled out from the shaft 1. For this reason, the spline ball 37 rolling in the spline groove 1b does not move to the thread groove 1a at the intersection A.

  FIG. 5 shows an enlarged perspective view (including a partial cross-sectional view) of the nut 2. The nut 2 is rotatably supported by the bearing 23. The bearing 23 includes an outer ring 21 and two rows of bearing balls 22a and 22b. The outer ring 21 is substantially cylindrical and has a flange 21b at one end in the axial direction thereof. The outer ring 21 is attached to the housing of the Zθ actuator via a flange 21b. For example, two outer ring grooves 21 a are formed on the inner surface of the outer ring 21. For example, two inner ring grooves 24 a facing the outer ring groove 21 a are formed on the outer surface of the nut 2. Two rows of bearing balls 22a and 22b are interposed between the outer ring groove 21a and the inner ring groove 24a so as to allow rolling motion. A seal 21 c that closes the gap between the outer ring 21 and the nut body 24 is attached to the outer ring 21.

  The nut 2 includes a cylindrical nut main body 24, circulating parts 25a and 25b provided at axial ends of the nut main body 24, and lid members 26a and 26b covering the circulating parts 25a and 25b. As shown in FIG. 6, the circulating components 25 a and 25 b are accommodated in the recess 24 e on the end surface of the nut body 24 in the axial direction. The circulating parts 25a and 25b are covered and fixed by ring-shaped lid members 26a and 26b. The lid members 26a and 26b are fastened to the nut body 24 by fastening members 30 such as screws.

  As shown in FIG. 5, a spiral ball screw groove 24b (hereinafter simply referred to as a thread groove 24b) facing the thread groove 1a of the shaft 1 is formed on the inner surface of the nut body 24 (see also FIG. 7). . A screw ball 27 is interposed between the screw groove 24b of the nut body 24 and the screw groove 1a of the shaft 1 so as to be able to roll.

  In the circulation parts 25a and 25b, a substantially arc-shaped direction changing path 28 for circulating the screw balls 27 is formed. The nut body 24 is formed with a linear through hole 29 penetrating in the axial direction. The direction change path 28 is connected to the thread groove 24 b and the through hole 29 of the nut body 24.

  The spiral load rolling path 20, the substantially arc-shaped direction changing path 28, and the straight through hole 29 between the thread groove 24b and the thread groove 1a of the shaft 1 constitute a circulation path. The direction change path 28 of the circulation component 25 a deflects the screw ball 27 rolling on the spiral load rolling path 20 in the tangential direction and guides it to the through hole 29. The screw ball 27 guided to the through hole 29 is returned to the load rolling path 20 again after passing through the direction changing path 28 of the circulating component 25b on the opposite side.

  FIG. 7 shows a cross-sectional view of the nut body 24 along the axis 1c. In a general ball screw, the depth d1 of the screw groove 1a of the shaft 1 is made equal to the depth d2 of the screw groove 24b of the nut body 24. On the other hand, in the present embodiment, the depth d1 of the screw groove 1a of the shaft 1 is made deeper than the depth d2 of the screw groove 24b of the nut body 24. This is to reduce the BCD (Ball Center Diameter, which is the ball center diameter, which is the diameter of the ball center O1 as viewed from the axial direction) of the ball screw including the shaft 1, the nut 2, and the screw ball 27.

  The cross-sectional shape of the thread groove 1a shown in FIG. 7B is a Gothic arch shape. The screw ball 27 contacts the screw groove 1a at two points P1 at a predetermined contact angle. The cross-sectional shape of the thread groove 24b is also Gothic arch shape. The screw ball 27 contacts the screw groove 24b at two points P2 at a predetermined contact angle. When the BCD is reduced, the depth d2 of the thread groove 24b becomes shallow, and there is a possibility that edge loading occurs. In order to avoid this, the BCD is made larger than the diameter d3 of the shaft 1 to prevent the thread groove 24b from becoming too shallow.

  FIG. 8 shows an enlarged perspective view (including a partial cross-sectional view) of the outer cylinder 3. The outer cylinder 3 is rotatably supported by the bearing 33. The bearing 33 includes an outer ring 31 and two rows of bearing balls 32a and 32b. The outer ring 31 is substantially cylindrical and has a flange 31b at one end in the axial direction thereof. The outer ring 31 is attached to a housing of a Zθ actuator, for example, via a flange 31b. For example, two outer ring grooves 31 a are formed on the inner surface of the outer ring 31. For example, two inner ring grooves 34 a facing the outer ring groove 31 a are formed on the outer surface of the outer cylinder 3. Two rows of bearing balls 32a and 32b are interposed between the outer ring groove 31a and the inner ring groove 34a so as to allow rolling motion. A seal 31 c that closes the gap between the outer ring 31 and the outer cylinder main body 34 is attached to the outer ring 31.

  The outer cylinder 3 includes a cylindrical outer cylinder main body 34 and ring-shaped circulation parts 35 a and 35 b attached to the axial ends of the outer cylinder main body 34. FIG. 9 is a cross-sectional view perpendicular to the axis of the outer cylinder 3. As shown in FIG. 9, a linear ball spline groove 34b (hereinafter simply referred to as a spline groove 34b) extending in the axial direction is formed on the inner surface of the outer cylinder main body 34 so as to face the spline groove 1b of the shaft 1. . Both of the cross-sectional shapes of the spline grooves 1b and 34b are circular arcs. A spline ball 37 is interposed between the spline groove 1b and the spline groove 34b so as to allow rolling motion. The spline ball 37 contacts the spline grooves 1b and 34b at one point. The contact angle of the spline balls 37 is set so that clockwise and counterclockwise torque can be applied by the four rows of spline balls 37.

  The outer cylinder main body 34 is formed with a linear return path 39 that penetrates the outer cylinder main body 34 in the axial direction in parallel with the spline groove 34b. The return path 39 is not arranged in the radial direction of the spline groove 34b (that is, on the line connecting the axis 1c of the shaft 1 and the spline groove 34b) in order to reduce the diameter of the outer cylinder main body 34. Placed near.

  A cage 41 is incorporated in the inner surface of the outer cylinder main body 34. The cage 41 holds the spline ball 37 so that the spline ball 37 does not fall off even when the outer cylinder 3 is pulled out of the shaft 1.

  As shown in FIG. 8, a U-shaped direction changing path 38 for circulating the spline balls 37 is formed in the circulation parts 35a and 35b. FIG. 8 shows a spline ball 37 that moves along a U-shaped direction change path 38, but the direction change path 38 is actually formed in the circulation parts 35 a and 35 b. The direction changing path 38 is connected to the spline groove 34 b and the return path 39 of the outer cylinder 3.

  A linear load rolling path 36, a U-shaped direction changing path 38, and a linear return path 39 between the spline groove 1b and the spline groove 34b constitute a circulation path. The circulation part 35a direction change path 38 deflects the spline ball 37 rolling on the linear load rolling path 36 into a substantially U shape and guides it to the return path 39 near the shaft 1. The spline balls 37 guided to the return path 39 are returned to the load rolling path 36 again after passing through the direction changing path 38 of the circulating component 35b on the opposite side.

  According to the present embodiment, the diameter of the screw ball 27 is made smaller than the diameter of the spline ball 37, although the depth of the screw groove 1a of the shaft 1 is deeper than the depth of the spline groove 1b. In the nut 2 and the outer cylinder 3, the outer diameter of the nut 2 tends to be larger than that of the outer cylinder 3 due to the difference in the circulation structure. This is because the nut 2 deflects the screw ball 27 rolling the spiral thread groove 1a of the shaft 1 in the tangential direction, whereas the outer cylinder 3 rolls the linear spline groove 1b of the shaft 1. This is because the moving spline ball 37 is deflected near the axis 1. According to the present embodiment, since the diameter of the screw ball 27 is smaller than the diameter of the spline ball 37, the outer diameters of both the nut 2 and the outer cylinder 3 can be reduced in a balanced manner. Splan can be made smaller and lighter.

  In order to increase the depth of the thread groove 1a of the shaft 1, it is necessary to either increase the diameter of the screw ball 27 or decrease the BCD. According to this embodiment, since the depth d1 of the thread groove 1a of the shaft 1 is deeper than the depth d2 of the thread groove 24b of the nut 2, the BCD of the ball screw is reduced. For this reason, the depth of the thread groove 1a of the shaft 1 can be increased without increasing the diameter of the screw ball 27.

  Since the BCD of the ball screw is larger than the diameter d3 of the shaft 1, it is possible to prevent the thread groove 24b of the nut 2 from becoming too shallow and the edge load from occurring in the thread groove 24b of the nut 2.

  Since the cross-sectional shape of the ball screw groove 1a of the shaft 1 is a Gothic arch shape, and at least a part of the cross-sectional shape of the spline groove 1b of the shaft 1 is a circular arc shape, the screw groove 1a of the shaft 1 is more than the spline groove 1b. Can be deeper.

  Note that the present invention is not limited to the embodiment described above, and can be changed to other embodiments without departing from the spirit of the present invention.

  In the above embodiment, the depth of the screw groove of the shaft is made deeper than the depth of the spline groove of the shaft, but the depth of the screw groove of the shaft can be the same as the depth of the spline groove of the shaft. . The screw balls are guided not only in the shaft thread groove but also in the nut thread groove, so even if they are the same, the thread ball is prevented from moving from the thread groove to the spline groove at the intersection. it can.

  In the above embodiment, the cross-sectional shape of the spline groove of the shaft and the outer cylinder is a circular arc shape, but may be a gothic arch shape. Moreover, although the cross-sectional shape of the screw groove of the shaft and the nut is a Gothic arch shape, it can also be a circular arc shape.

DESCRIPTION OF SYMBOLS 1 ... Shaft, 1a ... Ball screw groove of shaft, 1b ... Ball spline groove of shaft, 2 ... Ball screw nut, 3 ... Ball spline outer cylinder, 24b ... Ball screw groove of ball screw nut, 34b ... Ball spline of outer cylinder Groove, 27 ... Ball for screw, 37 ... Ball for spline

Claims (4)

An axis formed such that a spiral ball screw groove and a linear ball spline groove intersect each other;
A ball screw nut having a spiral ball screw groove facing the ball screw groove of the shaft, and enabling circulation of a screw ball engaged with the ball screw groove of the shaft;
A ball spline outer cylinder that has a linear ball spline groove facing the ball spline groove of the shaft and enables circulation of spline balls that engage with the ball spline groove of the shaft;
The depth of the ball screw groove of the shaft is equal to or greater than the depth of the ball spline groove of the shaft;
A diameter of the screw ball is smaller than a diameter of the spline ball ;
Making the depth of the ball screw groove of the shaft deeper than the depth of the ball screw groove of the ball screw nut;
A ball screw spline in which a BCD of a ball screw including the shaft, the ball screw nut, and the screw ball is made larger than a diameter of the shaft . An axis formed such that a spiral ball screw groove and a linear ball spline groove intersect each other;
A ball screw nut having a spiral ball screw groove facing the ball screw groove of the shaft, and enabling circulation of a screw ball engaged with the ball screw groove of the shaft;
A ball spline outer cylinder that has a linear ball spline groove facing the ball spline groove of the shaft and enables circulation of spline balls that engage with the ball spline groove of the shaft;
The ball screw nut is provided at a nut body in which the ball screw groove is formed and a through-hole penetrating in the axial direction is formed; and an axial end portion of the nut body; And a circulation part having a direction change path connected to the through hole,
The depth of the ball screw groove of the shaft is equal to or greater than the depth of the ball spline groove of the shaft;
A diameter of the screw ball is smaller than a diameter of the spline ball;
A ball screw spline that makes the depth of the ball screw groove of the shaft deeper than the depth of the ball screw groove of the ball screw nut .   The ball screw spline according to claim 2, wherein a BCD of a ball screw including the shaft, the ball screw nut, and the screw ball is made larger than a diameter of the shaft.   The cross-sectional shape of the ball screw groove of the shaft is a Gothic arch shape, and at least a part of the cross-sectional shape of the ball spline groove of the shaft is a circular arc shape. The ball screw spline according to one item.

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